Steel for plastic mold dies and articles made therefrom



Patented Aug. 9, 1949 STEEL FOR PLASTIC MOLD DIES AND ARTICLES MADE THEREFROM Peter Payson, New York, N. Y., assignor to Crucible Steel Company of America, New York, N. Y., a corporation of New Jersey No Drawing. Application March 13, 1947, Serial No. 734,554

Claims. .(Cl. 75-1128) This invention pertains to mold dies for the compression-molding of resinous plastics, and to a low carbon, low alloy chrome-manganese-molyceienum steel, which may also contain small amounts of either or both nickel and boron, and which is especially suited for use in mold dies of the character aforesaid.

Mold dies for the compression-molding of thermosetting synthetic resin powders, such as the phenol-, ureaor melamine-aldehyde resins, are made by hubbing, i. e., by pressing, into a relatively soft block, an impression of the resinous object to be molded therefrom. The hubbing is effected by means of a hard steel die which has been machined or engraved to the shape and configuration of the object to be molded, and which is impressed under tremendous hydraulic pressure into the aforesaid relatively soft steel die After the hubbing operation is completed, the resulting impression-containing die block is carburized, and then heat treated by a conventional quench and temper treatment.

The principal requirements of a suitable steel for plastic mold dies, are that 1) it must be easy Steel A can be annealed to a very low hardness and is easy to cold hub, but it has very poor hardenability and dies made from it have to be quenched in water with accompanying risk of 5 distortion in order to be hardened satisfactorily and even with a water quench the attainable hardness at the core of the die is quite low. Steel B has fairly good hardenability and dies made from it therefore, can be quenched in oil after they are carburized and attain high hardness at the surface and fair hardness at the core, but this steel is definitely inferior to steel A in hubbability. Steel C has excellent hardenability but even when it is fully annealed it is too hard for efiicient cold hubbing, and dies made from it have to be machine cut which is much more expensive than cold hubbing.

I have discovered an analysis of steel which is applicable for plastic mold dies, which can be cold hubbed almost as easily as steel A, and

which has hardenability much better than that of steel A and at least equal to that of steel B. I have balanced the composition of this steel so that'it contains in suitable proportions the eleto hub; (2) it must be susceptible to Icarburizamerits M and M0 which pp y tion; (3) it must have good harden'ab'ility so that after it is carburized, the die can be hardened by an oil quench, rather thana water quench in order that the case or carburized part of the provethe hardenability of the steel but which at the same time do not appreciably lower the hubbability of the steel. The elements least efliective in increasing the hardness of ferrite, and theredie Will have high hardness and. the core, or unfore the hardness of e fully ea ed steel,

car-burized part of the die, will have fair strength to support the case of the die under the rather heavy pressures of about one to four tons per square inch employed in the compression molding of resinous plastics; and (4) it must be inexpensive. Typical analyses of the steels most commonly used for this purpose hitherto are as follows:

which controls the hubbability of the steel, are Cr, Ni, Mo, Mn, and Si, in the order named. The elements most effective in increasing the hardenability of steel are Mn, Mo, Cr, Si, and Ni, in the order named. Therefore, for optimum results in in a steel for plastic mold dies I select the elements near the top of each list. I use an appreciable amount of Cr because it has least efiect on hubbability and an appreciable effect on hardena- 'bility. I use a small amount of Si, just sufiicient to assure adequate deoxidation of the steel, because this element has the most deleterious efiect on hubbability and little effect on hardenability. I use-intermediateamounts of Mn and Ni because 5 although Mn has a great efiect on hardenability it also seriously affects hubbability whereasak though Ni has a relatively minor eifect on hardenability, it also has a relatively minor effect on hubbability. I use a relatively small amount of Mo because although it has a, great effect on hardenability and a relatively small effect on hubbability, it is the most expensive of the elements in this steel. Finally I may use a very small amount of boron which has a relatively small effect on hu-bbability and an appreciable effeet on hardenability. High carbon has a serious efiect on hubbability and therefore it is kept as low as feasible, generally under 0.10%.

The broad range for my improved steel for plastics mold dies is:

Table III Steel Designation 51 211 D Plain carbon (per A) 89 F This invention 99 G .do 99 K .do 99 H rln 103 J d 107 E Lower Ni-Cr (per B) 109 L Higher Ni-Cr (per 0) 137 Further tests on hubbability were made by measuring the diameter of the impression made in Percent Percent Percent Percent Percent Percent Percent C Mn Si Ni Gr Mo B The preferred analysis is: the different steels with a 10 mm. ball under a load Percent Percent Percent Percent Percent Percent Percent 0 Mn Si Ni Cr Mo 13 As representative of the properties of steel within these limits, as compared to prior art steel of the character aforesaid, I submit the data below:

of 12,000 pounds. These were .325 in. for steel D; .305 for steel K; for steel E; and .265 for steel L.

To establish the relative hardenabilities of these Table II Per Cent Per Cent Per Cent Per Cent Per Cent Per Cent Per Cent Heat Steel 0 Mn Si i Cr Mo B Bal.

Of these, steel D is similar to steel A of Table I; steel E is similar to steel B; and steel L is similar to steel C. All the other steels are within the limits of this invention.

As fully annealed, the Brinell hardness values steels, samples were tested by the conventional Jominy end-quench procedure, for both 15001 and 16501 austenitizing temperatures. The hardness values attained at the 2, 6, and 10 sixteenth positions on the test pieces are as follows:

*Austem'tizing temperature, F.

of these steels, and it may be taken that the hubbabllity varies inversely as the Brinell hard aess, are as follows:

Further data on relative hardenabilities were,

- obtained by testing the hardness and tensile properties of some of these steels as quenched in 1" round bars and tempered at 350E with results as follows:

4. An alloy steel characterized by good hubbability and hardenability containing about: 0.02

Table V Steel Designation Treatment aits r. '51. Pefi ent pt'd'a A Plain Carbon 1450!, water qu 120 40,000 60,000 30 65 B Lower Ni-Gr 150013, oil on 160 50,000 80,000 30 65 K This invention", 1550], oil qu 160 4 ,000 81,000 26 62 Thus it has been shown that the steel of the to 0.15% carbon; 0.1 to 1.0% manganese; 0.8 to present invention has a better combination of 3.0% chromium; 0.1 to 1.0% molybdenum; from hubbability and hardenability than commercial an effective amount up to about 1% nickel; up to steels heretofore known. about 0.4% silicon; up to about 0.005% boron;

In the appended claims, by the expression and the balance substantially all iron. balance substantially all iron is meant iron 5. A hubbed, carburized and heat treated mold except for impurities within commercial tolerdie, made of an alloy steel containing about: 0.02 ances. to 0.15% carbon; 01 to 1.0% manganese; 0.8 to

I claim: chromium; 0.1 to 1.0% molybdenum; from 1. An alloy steel characterized by good hubbaan eiiective amount up to about 1% nickel; up to bility and hardenability, containing about: 0.02 about 0.4% silicon; up to about 0.005% boron; to 0.07% carbon; 0.3 to 0.5% manganese; 0.02 and the balance substantially all iron. to 0.2% silicon; 0.4 to 0.6% nickel; 1 to 2% chro- PETER PAYSON. mium; 0.15 to 0.25% molybdenum; 0.002 to 0.005% boron; and the balance substantially all REFERENCES CITED 1101'1. I11 1 2. A hubbed, carburized and heat treated mold :1; gfi is are of record m the die for molding resinous plastics, made of an alloy steel containing about, 0.02 to 0.15% car- UNITED STATES PATENTS bon; 0.1 to 1.0% manganese; 0.8 to 3.0% chro- Number Name Date mium; 0.1 to 1.0% molybdenum; up to about 1,519,333 Walter "D6816, 1924 0.4% silicon; up to about 1.0% nickel; up to about 2233399 Tisdale May 19, 1942 0.005% boron; and the balance substantially all 3332441 Fleischmann Oct 9 1943 iron.

3. A hubbed, carburized and heat treated mold OTHER REFERENCES die for molding resinous plastics, made of an Chemical Engineers Handbook, second edition, alloy steel containing about: 0.02 to 0.07% carpage 2113, Alloy No. 91. John H. Perry, editor. bon; 0.3 to 0.5% manganese; 0.02 to 0.2% silicon; Published in 1941 by the McGraw-I-Iill Book Com- 04 to 0.6% nickel; 1 to 2% chromium; 0.15 to pany, New York.

0.25% molybdenum; 0.002 to 0.005% boron; and the balance substantially all iron. 

